Insulin is a mammalian hormone essential for the utilization of glucose derived from food intake, from the blood system by the liver, muscle and adipose tissue. Insulin affects glucose, protein and lipid metabolism by binding to its receptor, which subsequently activates various cell signal transduction pathways that mediate the biological actions of insulin. Among the downstream effects of insulin binding is regulation of the glucose transporter GLUT4 that results in increased glucose uptake in skeletal muscle and adipose. Insulin also increases glucose utilization by affecting key enzymes involved in glucose metabolic pathways primarily at the level of transcription, and insulin increases glucose storage by activating signal transduction proteins in pathways leading to glycogen synthesis. Insulin maintains glucose homeostasis and reduces hyperglycemia by decreasing hepatic glucose production and release, and increasing glucose uptake, utilization, and storage in body tissues. Insulin directly affects glucose uptake in skeletal muscle and adipose tissue through its regulation of the GLUT4 glucose transporter. The liver is one of the major targets of insulin for glucose uptake, utilization, and storage, but insulin's effects on hepatic glucose uptake are different than in muscle and adipose. In response to insulin, hepatic glucose uptake is dramatically augmented due to increased activity of enzymes involved in glucose utilization and storage via pathways of glycolysis and glycogenesis. This leads to a decrease in the intracellular glucose concentration, and consequently, glucose enters hepatocytes via facilitated diffusion in response to the concentration gradient that forms. In contrast to GLUT4 in skeletal muscle and adipose, the hepatic glucose transporter (GLUT2) is insulin independent. Other downstream effects of insulin receptor activation include increased lipogenesis and increased protein synthesis.
Type 1 diabetes mellitus (DM) occurs when the body does not make enough or alternatively, does not make any insulin, thereby causing blood sugar levels to increase significantly after food intake, resulting in a condition known as hyperglycaemia. Extended periods of hyperglycaemia can result in excessive oxidation of fatty acids resulting in production of ketones which acidify the blood giving rise to a condition known as ketosis. Type 1 DM can be treated by insulin injections at dosage levels calculated to maintain blood sugar levels within a target range. However, if the insulin injections are not correctly balanced with food intake and exercise, blood sugar levels can fall to hypoglycaemic levels which if untreated, can result in coma and death.
Type 2 DM occurs when the body isn't able to properly metabolize the insulin it produces. Depending on the severity, Type 2 DM can be managed by: (1) diet and exercise, (2) oral intake of insulin or insulin mimetics, or (3) insulin injections. Mechanisms of action for the oral agents include stimulation of pancreatic insulin secretion (e.g., sulfonylurea compounds), inhibition of hepatic glucose production (e.g., metformin), enhancement of peripheral insulin sensitivity (e.g., thazolidinediones), and slowing the rate of carbohydrate absorption (e.g., α-glucosidase inhibitors). Each of the Type 2 DM therapies must be carefully managed to avoid incidences of hypoglycaemia and hyperglycaemia.
In the developed world, the prevalence of both types of DM continues to increase, as do the costs of providing treatment to DM sufferers. As a consequence, considerable research efforts have been and continue to focus on increasing the understanding of insulin activity in order to enable development of new DM management strategies, therapies and pharmaceuticals. Among recent developments is the identification and partial characterization of two separate inositol phosphoglycan molecules. In response to insulin, inositol phosphoglycan molecules are hydrolyzed from glycosylphosphatidylinositols that are found in cell membranes. Inositol phosphoglycan molecules are considered putative insulin mediators based on their ability to mimic a large number of the metabolic actions of insulin both in vitro and in vivo. Although the structures of the inositol phosphoglycan molecules have not yet been completely elucidated, one molecule contains myo-inositol and glucosamine, and the other contains D-chiro-inositol and galactosamine as core components. Inositol is a hexahydroxycyclohexane that is structurally related to glucose. There are nine isomers of inositol that differ in their position of hydroxyl groups. Myo-inositol is the most common occurring isomer in plants and animals whereas D-chiro-inositol is relatively rare. In addition to these core components, both types of inositol phosphoglycan molecules also contain neutral sugars and phosphate residues. The origin of the myo-inositol-containing inositol phosphoglycan molecules is thought to be myo-inositol-containing glycosylphosphatidylinositol, as both phospholipase C- and phospholipase D-mediated hydrolysis of glycosylphosphatidylinositol yield biologically active inositol phosphoglycan molecules.
The insulin-like activities of isolated inositol phosphoglycan molecules and their chemically synthesized analogues have been widely investigated and have been previously reviewed (M. Field, 1997, Glycobiology 7: 161-168; D. R. Jones and I. Varela-Nieto, 1998, Cell Biology 30:313-326). It is known that the myo-inositol-containing inositol phosphoglycan molecule stimulates lipogenesis, glucose transport, glycogen synthesis, amino acid transport, protein synthesis, and GLUT-4 translocation in in vitro model systems. It is also known that myo-inositol-containing glycosylphosphatidylinositol molecule stimulates P13K, MAPK activity, but inhibits GSK-3 activity. The MI-IPG is also able to regulate expression of PEPCK in rat hepatocytes.
The D-chiro-inositol-containing inositol phosphoglycan molecule has also demonstrated in vitro insulin mimetic effects including the activation of key protein phosphatases in pathways known to be stimulated by insulin. In particular, it has been demonstrated that the D-chiro-inositol-containing inositol phosphoglycan molecule activates pyruvate dehydrogenase phosphatase and glycogen synthase phosphatase. These enzymes play a key role in the regulation of glucose disposal by oxidative metabolism (glycolysis) and by the non-oxidative route of storage by glycogen synthesis, respectively.
The insulin-mimetic effects of both inositol phosphoglycan molecules have also been demonstrated in vivo. Both inositol phosphoglycan subtypes increased glucose incorporation into diaphragm glycogen in normal rats and reduced hyperglycemia in streptozotocin-induced (STZ) diabetic rats (L. C. Huang, M. C. Fonteles, D. Houston, C. Zhang, and J. Lamer, 1993, Endocrinology 132: 652-657). Prolonged infusion with D-chiro-inositol-containing inositol phosphoglycan molecule normalizes plasma glucose levels in STZ-induced diabetic rats to the same extent observed with insulin but without inducing hypoglycemia (M. Fonteles, M. Almeida, and J. Lamer, 2000, Hormone and Metabolic Research 32: 129-132).
There remains a continuing need to develop new methods and pharmaceuticals suitable for the treatment of DM. In particular, there is a need to identify and characterize new therapeutics that cause a reduction in blood glucose levels, particularly those that are simpler to produce and less expensive than recombinant or naturally sourced insulin derivates. It is well known that the seeds of buckwheat (Fagopyrum cymosum (Trev.) Meisn.) contain significant amounts of myo-inositol, D-Chiro-inositol, and galactosyl derivatives of D-Chiro-inositol isomers commonly referred to as “fagopyritols” (Horbowicz and Obendorf, 1994). Analyses of the soluble carbohydrate composition of buckwheat seeds demonstrated the presence of significant levels of at least two galactosyl chiro-inositol isomers commonly known as Fagopyritol A1 and Fagopyritol B1, at least two di-galactosyl chiro-inositol isomers commonly known as Fagopyritol A2 and Fagopyritol B2, and small quantities of a tri-galactosyl chiro-inositol isomer commonly known as Fagopyritol B3. It is also known that the soluble carbohydrate content of buckwheat seed includes about 40% sucrose and 40% Fagopyritol B 1. Furthermore, the fagopyritols are found primarily in the embryo portion of buckwheat groats.
U.S. Pat. No. 6,162,795 and related U.S. Pat. No. 6,492,341 disclose an isolated Fagopyritol A1, an isolated Fagopyritol A2, an isolated Fagopyritol B3, and methods for preparing substantially pure Fagopyritol A1, Fagopyritol A2, Fagopyritol B 1, Fagopyritol B2, Fagopyritol B3 from buckwheat. The methods comprise a first step of preparing a flour from buckwheat seed or seed components, followed by a second step of extracting fagopyritols from the flour using an alcohol or an alcohol/water solvent. It is noted that '795 defines “fagopyritol” being substantially free of other naturally occurring buckwheat components.
U.S. Patent Application Pub. No. 2006/0029690 discloses methods for extracting tartary buckwheat with 30% ethanol to provide a biologically active component for treatment of hypoglycaemia.
U.S. Pat. No. 6,451,353 discloses the extraction from buckwheat rhizomes, of compositions useful for treating cancers and/or respiratory tract ailments. The compositions provided are tannins and/or procyanidins.